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How are the 737’s elevator and aileron cables attached to their control tabs without impeding the control surfaces’ motion under hydraulic power?
The 737 (all versions thereof) is one of the few jetliners still in production to have any manual-reversion capability for its flight controls in the event of the loss of all hydraulic systems.  If hydraulic pressure is lost in both the A and B hydraulic systems, control tabs on the elevators and ailerons unlock, and the elevator and aileron control cables, which are directly attached to these tabs, deflect them to produce aerodynamic forces that move the elevators and ailerons in the desired direction.1  When hydraulic pressure is available in either of the two primary systems, the control tabs are locked to their respective control surfaces and move with them.
Thus, the control tabs - which are still attached to the control cables even when locked to the elevators and ailerons under hydraulic power - deflect in the opposite direction when the flight controls are being moved hydraulically compared to when in manual-reversion flight.  For instance, when a pilot commands up elevator in hydraulic flight, the elevator actuators move the trailing edge of the elevators, and of their control tabs, upwards, even as the control cables themselves are trying to pull the trailing edges of the elevator control tabs downwards (as would be necessary when commanding up elevator in manual-reversion flight).  How does the 737’s flight-control system prevent the forces generated by the hydraulic flight-control actuators from feeding back through the control cables (via their attachments to the elevator and aileron control tabs) and forcing the pilots’ yokes in the direction opposite their control inputs, or, alternatively, the forces exerted directly by the control cables from impeding the control surfaces’ motion when under hydraulic power?

1: Not all of the 737’s control surfaces have provisions for manual control; the spoilerons (which deflect asymmetrically to assist the ailerons in rolling the aircraft) are inoperative if the A and B hydraulic systems both fail, while the rudder (which provides yaw control independent of roll) can be powered by the third, standby hydraulic system2 if both the A and B systems fail, but does not have manual-reversion capability in the event of a failure of all three hydraulic systems.
2: The standby hydraulic system (which can provide hydraulic power to move the rudder, actuate the thrust reversers, and - if the ALTERNATE FLAPS switch is engaged - extend the leading-edge high-lift devices) is normally unpressurised, but can be manually activated by the pilots (and activates automatically in the event of a hydraulic failure during critical phases of takeoff and landing); this is generally done in the event of a failure of one or both main hydraulic systems, but the standby system can be engaged even if both the A and B systems are fully operational (useful for clearing some types of rudder jams, although less so nowadays than was the case with the 737’s pre-2008 rudder-control system).

Good question, I have wondered the same.

Short answer: The 737 doesn't have control tabs, per se (only geared tabs), so its aileron and elevator cables AREN'T attached to the tabs.  (That said, it would have been a valid question re: MD-90's elevator, for example, in which case some of the provided answers would have been correct and applicable.)

Welcome to AvSE!

Incorrect; the 737 does have elevator and aileron control tabs (although they're only actually used as such in manual-reversion flight), as detailed in the prior answer.


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Why are several of the Tu-104’s cabin windows oddly positioned?
The Tu-104 (the fourth jetliner to fly1 and the second to enter revenue service2) has a cabin-window layout that is... somewhat odd, to say the least.

From front to back:

What appears to be the second cabin window from the front (although, given how far forward it, and the window in front of it, are, I’m not sure that they are actually cabin windows; I’m not familiar with the location of the Tu-104’s cockpit bulkhead) is mounted so high on the side of the fuselage (the whole window is in the white region above the blue livery striping on the sides; in contrast, most of the Tu-104’s cabin windows are mounted near the middle of this blue band) that one would only ever be able to see the sky through it, unless something was going really wrong.  It and the one in front of it also appear to be slightly smaller than the windows further back, but this could just be perspective or a trick of the eye.
The two consecutive windows over the front middle section of the wing are mounted higher than the windows in front of and behind them, although not as high as the window discussed in point #1 (most of the area of these windows still falls within the blue area, with only the tops of the windows breaching the white).  The more forward of these two windows appears to form part of the second overwing escape hatch - but the window in front of it looks to be part of the forwardmost overwing exit, and, yet, is mounted at the normal height - and these two windows have Aeroflot’s winged hammer and sickle painted in the space underneath them - but I’m having a hard time believing that a simple livery detail would have any significant influence on the design of the aircraft itself (it’s usually the other way around!).
The fourth window from the rear is mounted about as high as the windows discussed in point #2.  It lies above the numeric portion of the aircraft’s tail number, but - again like with point #2 - I’m having great difficulty believing that the window placement was simpler to alter than the paint job.
Finally, the three rearmost cabin (I think?) windows are mounted very high on the fuselage - about as high as the window in point #1.  These three windows overlie the “CCCP” portion of the aircraft’s tail number (but, again, see points #2 and #3!).

Why the wonky window work?

1: ...preceded by the Comet, Jetliner, and Caravelle.
2: ...preceded only by the Comet.

From the various photos of this aircraft on Wikipedia, there is considerable variation in window placement between models too.

I found a cutaway diagram of the Tu-104B. It appears that, at least on this model, some of the seats in the middle were raised a bit to perhaps accommodate some engine parts (there appears to be a label on the diagram which I can't quite read). The windows were raised correspondingly to match the seats. The mid-positioned one at the aft may have been placed there to match one in a door on the port side of the aircraft. The three high-positioned ones appear to be windows in the toilets (туале́ты).

The raised overwing section is labelled simply '2nd cabin, 18 seats'. As far as I know, the floor was indeed raised to accomodate the wing spar. The front raised window is in the kitchen (on the right) and entrance (on the left); the 3rd section is 'entrance/cloak room' (the windows are higher presumably because people never sit there). This is, by the way, a later 'economy' cabin design with 100+ setas; earlier versions had about 50 seats in what we would now call 'business' class (but there were no 'classes' on domestic flights in the USSR).

So the answer is "To create a tripping hazard, of course!"

The seats in the middle are raised to accommodate the centre wing-box. Probably bigger/heavier than normal as the engines are mounted close to the wing root.
For the forward window, it looks like theres a work area opposite the entry door so the window would let in some light.

The forward window could also be for Star based navigation, it probably has a dedicated navigator station with a sextant for positioning at night.

The dedicated navigator station was in the fully glazed nose cone on Tu-104.

Not easy getting a star-sight from the nosecone. It was also common to have it on the upper centreline to give the biggest field of vision.. also the glass/perspex needed to be optically perfect to avoid misreading.. another reason the sighting from the nosecone may not work.

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Two aircraft with same air speed, blank angle, but different mass, are the radius of turn the same?
Two aircraft with same airspeed, blank angle, but different mass, are the radius of turn the same?

What have you done to try and answer this homework question by yourself? Where are you stuck?

Are the aircraft the same type? Same wing configuration?  Are they flying at the same altitude and speed?

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Lateral Stability- Why aircraft will not return of its own accord to the original heading after a sideway gust?
I am reading the Stability section of FAA it says:

If an aircraft is flying in a straight line, and a sideward gust
of air gives the aircraft a slight rotation about its vertical
axis (i.e., the right), the motion is retarded and stopped by
the fin because while the aircraft is rotating to the right, the
air is striking the left side of the fin at an angle. This causes
pressure on the left side of the fin, which resists the turning
motion and slows down the aircraft’s yaw. In doing so, it
acts somewhat like the weather vane by turning the aircraft
into the relative wind.
The initial change in direction of the
aircraft’s flight path is generally slightly behind its change
of heading. Therefore, after a slight yawing of the aircraft
to the right, there is a brief moment when the aircraft is still
moving along its original path, but its longitudinal axis is
pointed slightly to the right.

The aircraft is then momentarily skidding sideways and,
during that moment (since it is assumed that although the
yawing motion has stopped, the excess pressure on the left
side of the fin still persists), there is necessarily a tendency
for the aircraft to be turned partially back to the left. That is,
there is a momentary restoring tendency caused by the fin.
This restoring tendency is relatively slow in developing and
ceases when the aircraft stops skidding. When it ceases, the
aircraft is flying in a direction slightly different from the
original direction. In other words, it will not return of its own
accord to the original heading; the pilot must reestablish the
initial heading.

I am not quite understanding the last section: why aircraft will not return of its own accord to the original heading after a sideway gust?

The paragraph is actually talking about directional static stability, or yawing moment due to sideslip angle β ($C_n$β as aerodynamic coefficient). A positive directional static stability tends to return the aircraft to zero sideslip (β=0) if any sideslip disturbance occurs, due to the lift and drag generated by the vertical tail if any β is present.
The lift and drag by the vertical tail also creates a side force ($C_Y$β as aerodynamic coefficient) that offsets the velocity vector. So when β is reduced to 0, the heading has also changed due to a change in velocity vector.

Maybe an easier way of understanding this is to consider the case where the gust doesn't end.
This is called "crabbing" from the ground reference but the plane will simply fly a heading and the ground track is a combination of the airspeed and wind vectors.
Now back to the "gust".  Before it hits the plane is on on ground track based on the wind (could be 0) and it's airspeed.
The gust changes the relative wind so the planes directional stability tries to align it in a new direction.
As the gust passes, only thrust is acting on the plane.  Relative wind returns to the longitudinal axis of the aircraft, but the gust has caused some lateral rotation, or yaw.
Once the gust forces are gone, the plane flies straight away in a new direction.  It would take an equal gust, from the opposite direction, or control inputs, to return it to its original course.


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Why jet stream is stronger in winter?
I notice in a website taling about jetstream
https://www.weather.gov/jetstream/jet
It says:

The winds blow from west to east in jet streams but the flow often shifts
  to the north and south. Jet streams follow the boundaries between hot
  and cold air. Since these hot and cold air boundaries are most
  pronounced in winter, jet streams are the strongest for both the
  northern and southern hemisphere winters.

Why these hot and cold air boundaries are most pronounced in winter? I dont get it.

This would be a better fit for earthscience.stackexchange. The jetstream is of course important for aviation, but explaining why it occurs or when it is stronger is not really aviation related.

Jet streams are influenced by the horizontal temperature gradient between two air masses which creates what is called a "thermal wind component", which when supplemented by the actual wind movement, creates the local acceleration of wind running along the top of the frontal boundary into a jet (above 90kt), and which is always nestled into the warm air side, in the wedge of warm air just under the warm air tropopause.
The strength of the jet is therefore influenced by the temperature difference between air masses.  In winter the airmass boundaries (in North America) tend to move south, and the temperature differentials increase compared to summer.  With the higher temperature differentials and higher horizontal temperature gradients, the stream velocities tend to be stronger and they reside farther south.
If you really want to understand aviation weather theory, the absolute best book for this is the Royal Canadian Air Force Weather Manual. Can't recommend it highly enough.


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Why is the Constellation's nose gear so long?
The Lockheed Constellation has an enormously long nose gear, which causes the aircraft to slant appreciably backwards when sitting on the ground:
L-049

(Image by Greg and Cindy at Flickr, modified by Cobatfor at Wikimedia Commons.)
L-649

(Image by the San Diego Air and Space Museum, via Flickr, via Wikimedia Commons.)
L-749

(Image by RuthAS at Wikimedia Commons.)
L-1049

(Image by RuthAS at Wikimedia Commons.)
L-1649

(Image by Robert Togni at Flickr, via JuergenKlueser at Wikimedia Commons.  Note that, due to the gigantic nose gear, the fuselage is approximately level, despite the ground sloping downwards considerably towards the aircraft's nose.)
In contrast, other airliners of the era had a much-less-ridiculous nose gear length, like the DC-7:

(Image by Ted Quackenbush at airliners.net, modified by Fæ at Wikimedia Commons.)
and the Stratocruiser:

(Image by Bill Larkins at Flickr, via Wikimedia Commons.)
Why is the Constellation's nose gear so much longer?

The Connie is one of the most beautiful airplanes ever IMO, saw several when they came in to the EAA one year, really graceful in the air.

The original L-049 prototype had a much stubbier nosegear but test pilots Eddie Allen and Kelly Johnson quickly discovered that it did not reach the ground.

From the picture, it seems like the main gear of the Constellation is also quite a bit taller than the others.  Maybe the designers were concerned about prop clearance on rough fields?

The Connie's fuselage has a subtle S shaped contour which was intended to conform somewhat to the upwash ahead of the wing and downwash aft of the wing, with a final upturn at the end to place the horizontal tail at the desired vertical location.

They also tapered the fuselage to the smallest cross sectional area possible at the nose, to part the air gently you might say, so the bottom ends up sloping up toward the nose.
Then you have main gear legs that are fairly long because the R3350's propellers are quite large.
The wing incidence is set to optimize the fuselage curvature's presentation into the airflow in cruise.
At the same time, you want to have wing chord in a certain desirable AOA range sitting on the ground, and you want to keep the tail from sitting too high (the Connie has the 3 surfaces to keep the vertical height of the tail low enough to fit the common hangars of the day).
Combine all those factors together and you end up having to the make the strut really long, and ending up with the most graceful airliner ever designed.

I already knew about the streamlining and the tail-height restrictions, but now I see how that necessitates tilting the fuselage back slightly!

Could you expand on having the wing at a desirable AOA on the ground?

The wing's angle-of-attack while rolling on all three wheels. You want to be close to zero or minimal lift with the nosewheel down but not have to rotate too far to get AOA for lift off.

You can see that the underside of the Connie's fuselage ahead of the wing root is contoured upwards to begin the taper which ends at the tip of the plane's nose. The other planes had constant-section fuselages ahead of the wing root, in which the nose does not begin to taper down until just aft of the cockpit.
To maintain the same propeller tip ground clearance, the Lockheed design then required a longer nose gear strut because the attach point for the nose wheel was higher in the air.
(In the case of the Douglas aircraft, maintaining a constant fuselage cross-section forward and aft of the wing reduced tooling costs and enabled fuselage stretches in future revisions of the airframe.)


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How is the debris deflector on the DC-9-80 ("MD-80")'s nose gear kept from striking the ground during landing?
The DC-9-80 (marketed as the "MD-80") has, mounted to its nose gear, what I presume to be a debris deflector (a sled-shaped device to keep the nose gear from kicking up pieces of gravel or asphalt or zombie hands that could dent or puncture the fuselage or wings or get sucked into an engine).
This presumed debris deflector seems to extend almost as low as the bottom of the nosewheels themselves:

(Image originally by Anthony92931 at Wikimedia Commons; cropped and annotated by me.)
It seems to me, with a debris deflector mounted that low down, that, upon derotation, the nosegear tyres could easily compress enough for the deflector to strike the runway surface, which would cause it to experience very rapid wear, and could conceivably tear it completely free of the aircraft (thus adding to the debris problem, rather than mitigating it).  How is this avoided?

Out of curiosity, what made you think that the answer would be different from "it is actually high enough"? Is there any particular reason? I don't want to be argumentative or anything, I am just curious.

@VladimirCravero I think the OP wonders whether they are missing something. E.g., is the lower part made of rubber (seems possible looking at the photo in ymb1's answer)? Does it magically move somehow?

If you compress the nose tires enough for that thing to hit you will have broken other parts and rapid wear of the device will be the least of your concerns.  Aircraft tires are pretty high pressure and don't have a lot of give to them.  (excepting tundra tires on bush planes)

@Peter-ReinstateMonica: She, not they, but yeah, that's pretty much what I was wondering.

@Vikki Wow, it's been a while since this comment! Glad to know I had the right hunch here (it looks weird to me as well, as if it should rub on the runway). As an aside: I didn't get the pronoun right though; I didn't look at your profile. I thought "they" covers all genders? Non-native speaker here trying to do the right thing ;-).

@Peter-ReinstateMonica: "They" is a generic pronoun usable for people of unknown gender; however, if the person in question's preferred pronouns are known, said pronouns should be used (in this case, she/her).  No hard feelings. :-)


text:
What were the Concorde's emergency procedures for an uncommanded droop-nose extension in flight?
The Concorde had a droop nose, which swung down during taxi, takeoff, and (especially) landing, so that the pilots could see where they were going without the long nose getting in the way.  During cruise, the nose was raised to the horizontal faired position, and held there by a pair of mechanical latches; the nose (as well as a heat-resistant visor that slid in and out of the nose) were normally raised and lowered by means of hydraulics, but could also be dropped by means of gravity if need be.
While obviously essential for landing, takeoff, and (to a lesser degree) taxiing, I'd imagine that the nose drooping uncommanded during supersonic cruise (for instance, due to a failure of the nose uplocks, or a nose droop actuator hardover sufficient to break the latches and force the nose down) would have been a Bad Thing, due both to the nose-down pitching moment generated by the drooped nose1 and to the windscreen suddenly no longer being protected from the superheated air flowing over the aircraft (probably in addition to some other things that I haven't thought of).

1: I've no idea if this would be sufficient to cause a loss of control if it happened during supercruise, but it could hardly have been a good thing.

I'm not sure there are procedures available to read online, but I'm pretty sure that the answer is "reduce speed"...

I don't know if there was a procedure written down, but I'm pretty sure if it were me, I'd want to reduce speed anyway in such a situation...

Anonymous downvoters #1 and #2, show thy faces.


text:
Can any helicopters use negative collective to descend rapidly?
On a helicopter, the collective is used to adjust the attack angle of all the main-rotor blades in the same direction by the same amount, causing the amount of lift generated to increase or decrease symmetrically across the whole main rotor, which, in turn, causes the helicopter to climb or descend.  If the collective is pulled all the way down to zero, the main-rotor blades move to zero attack, generating no lift (this is useful when on the ground).
Negative collective, if possible, would cause the main-rotor blades to move to a negative pitch, causing them to generate negative lift and accelerate the helicopter downwards.  This would enable a very rapid descent, which could be useful in certain circumstances (for instance, in combat).  Can any helicopters actually do this?

If this was possible, it would be a potential failure mode of the control system. That would be bad.

How often do you think you might need or want to fall faster than 32ft/sec squared?  Dumping power and pitching full forward is aggressive enough, I can't imagine how much stress it might put on the rotors to suddenly go to negative pitch...

Well, there actually are a few helicopters that can do this, such as the Westland Wasp and the Lynx. But as far as I'm concerned, it is not used to increase the rate of descent, but to "suck" the helicopter stuck to ship decks, which is how they manage to stay stable on the deck after landing in rough seas. You've probably seen some of those videos on YouTube, if not, here's a good one:

What I'm wondering about myself, is if this is somewhat normal for many "naval helicopters", such as the SH-60 Seahawk, or if it is exclusive to very few aircraft such as the two I mentioned earlier.

That landing is a compelling case for drone development!

That video is a compelling case for not going to sea! Oof, so little desire to experience that...

@EarlGrey. humans seem to still be quite a bit better at handling the controls than computers.

@JanHudec yes :) , it is not the human handling I am worried (in fact I am for pushing the drone development, we are not yet there), but it is the sea that worries me, it can suddenly sweep the boat or the helicopter and the lives aboard .

@JanHudec: If a drone crashes into the sea or goes over the side, big deal.  If a crewed helicopter crashes into the sea or goes over the side, ready the lifeboats, call SAR, and start thinking about what you might end up writing to next-of-kin.

Pic source
Negative thrust, as in enabling the helicopter to fly upside down...but no, the aerobatic Red Bull helicopter does not perform sustained inverted flight, it does barrel rolls and loops which maintain positive n.
Providing negative collective is not a design feature in helicopters. Ray Prouty briefly discusses sustained inverted flight in Helicopter Performance, Stability & Control, commenting on the extra collective travel required for negative collective pitch:

No actual helicopters are rigged in this manner, for two reasons. First, it would require a collective control system with twice the normal travel...Second, it would lose the important safety feature of having the down collective stop approximately corresponding to the right position for autorotation.

Upon a power failure, the collective needs to be lowered into the autorotation position within a couple of seconds, to prevent the rotor from losing RPM. With the collective down stop at correct autorotation position, the blade profiles must retain positive angle-of-attack, like in the pic below from the pretty good description on this site.

It seems that the autorotation setting at the collective down stop is a way more important design feature than negative thrust. Which would also bend the blades towards the tail boom, with possible catastrophic results.

What you describe for autorotation (the rotor blades being sucked forwards by their own lift) requires an airfoil with negative induced drag, which is physically impossible.

@Vikki It’s a matter of torque balance of the blade. Hard to visualise, reasonably described in the linked article.

@Vikki autorotation is similar to gliding with fixed wings—the airfoil has slightly negative pitch relative to the horizon, so it produces thrust, but because it is descending, still slightly positive angle of attack, so it produces lift. The image is wrong.

A helicopter applying downforce through its rotors would fall faster than a rock dropped next to it. Pulling out of that manoeuvre would demand excessive lift forces. Helicopters are not stressed for high manoeuvrability in the same way that some aircraft are, as the various forces imposed on the spinning rotor blades and driveshaft bearings would demand excessive strengthening and added weight. Only a few can even pull low-gee party tricks such as barrel rolls or loops.
Also, being in an effectively upside-down state, the helicopter would no longer have pendulum stability and would become dynamically unstable.
In autorotation the air flows up through the rotor disk. I don't know if any designs can set the blade incidence negative with respect to the disk, but even if they can the blade will still have a positive angle of attack to the oncoming airflow.

Pendulum stability is a fallacy

@Koyovis Only partly. It does affect the flight dynamics, though not in the simplistic manner often assumed. For example accelerating forwards will tend to push the nose up instead of down.

It affects flight dynamics. You make a statement about pendulum stability, which is a fallacy.

@Koyovis The fallacy is in its assumed effect. Were pendulum stability a fallacy per se, fixed-wing aircraft with high wings would not be given anhedral in order to reduce its excessive effect. This is not the place for a fuller discussion. You have offered your comment and I have replied. That is enough.

The comment is meant for insights that may have been missed, for amending the answer. I won't discuss it any further, since the speed stability of an underslung rotor  is clearly explained.


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Why was the Graf Zeppelin's endurance when fully fuelled with both fuels less than the sum of its endurances with each fuel separately?
The LZ-127 Graf Zeppelin used a unique dual-fuel system, with both a gasoline tank and a set of gas cells filled with blau gas; the airship could be flown using either fuel or both.  The purpose of using blau gas, instead of solely gasoline, was to reduce the amount of hydrogen that had to be valved off for buoyancy-compensation purposes, by reducing the amount by which the airship's buoyancy changed as fuel burned off.1
As might be expected, the airship's endurance was highest when both the gasoline tank and the blau gas cells were fuelled to capacity; however, the figures Wikipedia gives for the LZ-127's endurance using one, the other, or both fuels are somewhat odd, to say the least:

[...]  Some flights were made using only Blau gas carried in the dozen power gas cells which enabled the airship to cruise for up to 100 hours. Using gasoline alone it was able to cruise for 67 hours, and up to 118 hours using both.  [...]

100 + 67 = ...118?
One would expect that the airship's endurance with both fuel systems filled to capacity would be the sum of the endurance using only blau gas (100 hours) and the endurance using only gasoline (67 hours), which would total 167 hours (100 + 67), or 49 hours greater than what was apparently the actual endurance when using both fuels.
Am I missing something here?

1: Whereas gasoline is much denser than air (and its consumption thus greatly increases the airship's buoyancy), blau gas is only slightly denser than air, and, thus, its consumption alters the airship's buoyancy only slightly.

Not sure what gas the tank is filled if not blau gas. 100 hours may come from blau gas in gas cell, and air in gasoline tank, while 67 hours from hydrogen in blau gas cell, and gasoline in gasoline tank. But if you fill gas cell with blau gas, you can only fill 18 hours worth of gasoline or the ship is overweight?

Searching for the "Tsiolkovsky blimp equation", analog of Tsiolkovsky rocket equation, but so far no luck ;-)

Graf Zeppelin LZ-127 carried 75,000 cubic meters of hydrogen and 30,000 cubic meters
of Blau gas, which has a similar density to air.  This helped them avoid buoyancy issues when fuel was consumed.
With gasoline, the extra weight had to be compensated with more hydrogen, hence less room for Blau gas.
But I wonder if they could burn some of the hydrogen as fuel instead of venting it when the gasoline was being used up.  This would increase the range considerably.

There were no means of pumping hydrogen to the engines on LZ 127.


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Going from VFR in Class B to IFR
If I departed a heliport in Class B airspace, on my way out can I tell approach that I want to cancel my VFR flight plan to pick up an IFR flight plan?
I figured I could because Approach will be controlling me while I'm in the Class B airspace but I want to make sure before I request it.

Welcome to aviation.SE! Which country or regulations are you asking about?

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text:
How HF wire antennas on older aircraft are protected from lightning and static discharge?
For HF antennas installed on some older aircraft with wires running from points on the fuselage to the tail, what precautions are used to prevent lighting strikes or P-static accumulation from damaging the HF antennas or interfering with the communications? Are the wires shielded and would that be enough to prevent damage if lighting strikes?

This might also be a question for https://electronics.stackexchange.com/, since it's about electromagnetic protection of electronics.

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text:
Is there a speed needed to achieve flight?
Is there a minimum speed needed for flight (universally)? For example, if something was going 10 miles per hour, could it achieve flight? And by flight I don’t mean throwing a paper airplane, I’m talking about the item going to that speed, then flying.
Is there a formula for calculating the speed needed for flight?

You may want to narrow this down a bit. Helicopters, lighter than air ships, and VTOL aircraft can achieve flight with 0 forward speed. If you are strictly asking about heavier than air, fixed wing aircraft the answer is different.

Definitely a legitimate question even if it appears to be a beginner question but I agree with @Dave here that it could be narrowed down a bit.

The pedal-powered Gossamer Albatross crossed the English Channel (22.2miles) in 2.81 hours meaning that it had an average speed of just under 8mph. So to your point about 10mph, absolutely you can achieve flight below 10mph, not terribly practical flight in terms of speed, carrying capacity or range but technically and demonstrably possible.

It depend how you define speed, aircraft measure their speed relative to the air since this is handy to know when computing the lift generated and stall speed. However humans tend to be more interested in groundspeed, so the distance the aircraft travels over the earth per unit of time. Airspeed vs Groundspeed in practice:
https://youtu.be/WPyCywd4o5E?t=43s

There may be an ultimate lower bound, about where the ratio of random air motion to forward motion is near 1:1. But that is an extremely slow speed.
I've seen competitive balsa-wood gliders, weighing just a few ounces, achieve flight from a rubber band, going less than 1 mph, or a slow walking speed.
If the craft is light enough, the wings are big enough, and a little air is moving over them, lift is generated.

Thanks, sorry if it wasn’t detailed enough. I’ll my best to detail it. Say an item was going 10 miles per hour, had wings, etc, basically an airplane (except small enough to fly) could anything with the correct wingspan, etc, fly under its circumstances?

https://m.youtube.com/watch?v=ZqNEoeOKH8s

This is exactly what I was looking for, thanks!

Not even 'a few ounces': the F1D planes (like in the second video in the comments) weigh on the order of 1 gram!

I suppose the most basic formula for flight is $F=ma$. Whether flying or not, your aircraft feels a force called weight (m is the mass of your aircraft and a is the acceleration felt due to gravity). In order to fly, your aircraft needs to create enough lift to equal or exceed the weight. The formula for how much lift is created is $$L = \frac{1}{2} d v^2 s C_L$$
L = Lift, which must equal the airplane's weight in pounds
d = density of the air. This will change due to altitude. These values can be found in a I.C.A.O. Standard Atmosphere Table.
v = velocity of an aircraft expressed in feet per second
s = the wing area of an aircraft in square feet
CL = Coefficient of lift, which is determined by the type of airfoil and angle of attack.
Check out this video for a more detailed explanation. Your formula is at 4:45

NASA page with more details:
https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/lift_formula.html


text:
Why are RVR values reported in good visibility?
I just pulled the METAR for KLAX. Why are they reporting an RVR value for runway 25L if visibility is 9 statute miles?
KLAX 281553Z 00000KT 9SM R25L/2400VP6000FT FEW012 FEW045 18/08 A3000 RMK AO2 SLP157 FU FEW012 FU FEW045 T01780083 $

Because it's an automated system, so it follows a standard format... And it looks like it needs servicing.

Thanks for the reply, but RVR is usually not reported at KLAX from what I've seen in the past.

It's possible that when the "I need servicing" indicator is there, it may report everything by default in case one sensor is bad.

RVR and visibility is not the same thing. Besides, in theory, the general visibility could be good, while the RVR for a specific runway could be bad due to a local fog patch etc. Depends on the placement of the sensors.

It looks like that METAR was corrected to

KLAX 281553Z COR 00000KT 9SM FEW012 FEW045 18/08 A3000 RMK AO2 SLP157
  FU FEW012 FU FEW045 T01780083 $

Note the COR for corrected. The corrected METAR does not include RVR.
Including a screen grab of aviationweather.gov in case they dont keep the info up for a long time.


text:
Does a turbojet aircraft restriction on a SID or STAR also apply to turbofan aircraft?
Just wondering since I've never seen turbofan aircraft mentioned on SID or STAR charts, and many airliners are turbofan nowadays.

The term "turbojet" in this context is used a bit more loosely. The pilot-controller glossary document from the FAA defines it as follows:

TURBOJET AIRCRAFT− An aircraft having a jet engine in which the energy
  of the jet operates a turbine which in turn operates the air
  compressor.

You can see this is general enough to include turbofan aircraft as well. The main distinction is vs. a turboprop, where the turbine drives the propeller.


text:
What is the difference between an RNAV and a GPS approach?
How does the FAA decide to name an approach an "RNAV" approach or a "GPS" approach?
Is it because for RNAV approaches, there is the option to use something besides GPS like an inertial navigation system based on ground NAVAIDs vs GPS which actually requires use of the US maintained and monitored GNSS GPS system?

Are there specific approaches you have in mind?  As of right now, all new GPS approaches should be named RNAV (GPS) ...

I think the convention going forward is to unify the name to "RNP Approach"


text:
Is it okay to use magnetized tools on airplanes?
Let's say you stored your tools on a magnetic organizer in your toolbox, such as the one pictured.
Now you go and use a socket or wrench that is slightly magnetized. Have you done wrong?

mmm...free snack!

... what are you even using these tools for?

Just dont bring strong magnets on board during the test flight and wonder why you're flying in circles!

The answer: In most cases, no. There are a few exceptions.
The most common exception is when adjusting any sort of magnetic compass system. Flux valves, whiskey compasses, etc... are usually supposed to be adjusted with tools made of brass.
Even then, your typical A&P will adjust the whiskey compass, for example, wait for the thing to stop spinning like crazy, and then make a slight adjustment back the other way. He'll repeat that process until he gets it right. I'm not saying it's right, but it's what most of them do.
The only other scenario I can think of would be bringing those tools too close to a CRT-based display system. Magnetized tools can make the display go a little wacky.
There may be others, but that's all I can think of off the top of my head.

I brass screwdriver is only $10. If your A&P is using a non-brass one, you need to get a new A&P.


text:
What are the specifications of the General Electric J85 engine compressor?
On the internet I can't seem to find all the specifications I need.
Mostly I'm looking for the tip and hub radius and the angular velocity of the blades.
Thanks.

That's probably going to be beyond the scope of most on this board.  If you really want an answer to this, I'd contact Thornton Aircraft Company in Van Nuys, CA (http://www.thorntonaircraft.com).  They deal in sales and maintenance on old T-38s and F-5s as well as do type ratings in the jets.  They are intimately familiar with the J-85 power plant and could probably supply you with that info.


text:
How does an airspace class change from E to D affect already airborne aircraft?
In the US, there are some airports with a part-time tower. When the tower is in operation, the airspace around the airport is class D and requires communication with the tower. When the tower is closed, the airspace would be either class E or G (depending on height AGL) and pilots would land at the airport like they would an untowered airport. (Right?)
Assuming that is true, what happens to traffic already in the area when airspace becomes class D with communication requirements? Are the pilots supposed to "evacuate" the airspace before when it becomes class D? Or are they "adopted" by the tower when it opens?
If they are "adopted" what is that process and communication like?
If there is already a "busy" class E & G pattern (maybe with 3 airplanes in the pattern and one having just touched down) in process, what would we be likely to hear from the tower as they open? (Are there any separation requirements that class D airspace control would be trying to meet that a "busy" class E/G traffic pattern would not meet?)


text:
What is the difference between a flow and a checklist?
Use of checklists is a 'special emphasis area' during FAA private and commercial checkrides but there are a lot of comments in pilot forums about using flows instead, often - but not always - in the context of airline operations.
What is a flow, and what is the difference between a flow and a checklist? When should a pilot prefer one or the other? Or are they used together?

The difference is that the pilots who rely on "flows" waste less time on the gound but have a lot more accidents and "incidents" compared to people who use checklists.

@TylerDurden Another difference is pilots who rely (solely) on "flows" without backing them up with a checklist will  probably fail a lot of checkrides because they didn't use the checklist.

Generally speaking a checklist is an actual list of items to check, and a flow is a pattern of movement across the aircraft controls (switches, dials, etc.) which will accomplish some subset of the items on a checklist.
A flow should be essentially "muscle memory" for a pilot and performed by rote, where a checklist may be more detailed and include more specific guidance.
As you can probably tell flows and checklists are closely related (with flows usually being derived from checklists). The two are complimentary tools that are used together: A pilot will follow a flow, and then verify that the required items have been completed using the checklist.
In larger/more complicated aircraft it's not possible to fully memorize some of the checklists, so flows are used to accomplish the "red box" immediate action items before proceeding to the full checklist.

As a simple example, consider the engine power loss flow & checklist for a Piper Cherokee.
Engine Power Loss Flow (Red Arrow & Numbers)

Mixture (Set appropriately - usually "Rich")
Throttle (Set appropriately)
Carb Heat / Alternate Air (On)
Magnetos (Both)
Electric Fuel Pump (On)
Primer (In & Locked)
Fuel Selector (On a tank that has fuel)

Manufacturer's Engine Power Loss Checklist (Blue Numbers)

Fuel Selector - Switch to a tank containing fuel.
Electric Fuel Pump - On
Mixture - Rich
Carb Heat - On
Engine Gauges - Check for an indication of the cause of power loss
Primer - Check Locked.
If no fuel pressure is indicated  check tank selector position to be sure it is on a tank containing fuel.
Ignition Switch - "Left" then "Right" then back to "BOTH."
Throttle and Mixture - Different settings.
(This may restore power if problem is too rich or too lean a mixture, or a partial fuel system restriction.)
Try another fuel tank.
(Water in the fuel could take some time to be used up, and allowing the engine to windmill may restore power. If power loss is due to water, fuel pressure indications will be normal.)

In this example the flow accomplishes nearly all the checklist items, but it does so moving over the panel in one direction. As a practical matter the flow is accomplished by just moving your hand along the bottom of the panel: "Push the mixture. Push the throttle. Pull the carb heat. Twist the mag key. Flip all the switches UP (on). Pull the primer and make sure it doesn't move. Move the fuel selector lever to the other tank."
Completing the flow takes less than 10 seconds and can be done with one hand while your other hand is pitching for best glide speed.
The manufacturer's checklist for an engine power loss moves around the panel in a more haphazard way, but it also adds a few items (checking the engine gauges & fuel pressure indication), and provides more specific guidance on possible causes like fuel contamination (water in the fuel) & how to deal with them. These items could be important if the memory items from the flow don't restore engine power, assuming you have time (altitude) to spend troubleshooting them.

Definitions
A flow is like a fluid movement in specific directions across panels for a specific purpose, to set up the airplane. It is meant to be a muscle memory method.
Example:

A checklist is a "to do list", which ensures that important and/or required steps are taken for a particular tasks.

Why one is chosen?
Flows are used to go through all checks of the aircraft without running through an actual checklist. Flows are to be memorized mostly by muscle memory, and kept at least semi-congruent in their execution.
Can they used together?
Yes.
A flow contains information about how to quickly set up the airplane during different phases of flight. Pilots can speed through the steps of a flow. A flow may not be identical each time and can change according to situation, without omitting necessary steps.
Flows can be verified by checklists to ensure that they are complete. Once pilots follow items in a checklist overtime, they will memorize the key steps required for a particular task.
Final words
Flows can be rushed, checklists cannot. Steps can be omitted in flows, steps cannot be omitted in checklists.

Further Reading:

The mystery of flows vs checklists
Checklists and Flows
Flow vs. Checklist Your $.02
Checklist Discipline

Flows do not and have never been a replacement for the checklist. Airlines train flows for efficiency and safety. A flow is followed by a checklist in every phase of flight. If an item is missed on the flow the checklist catches it. Flows are SAFE and efficient. All of the U.S. airlines teach flows that must be memorized and followed by the checklist.

I would add that a flow is a rote memorized set of tasks based on manufacturer's checklists which need to be accomplished within a short amount of time to ensure vital systems in each phase of flight are set and working properly.  They are utilized during time and work critical phases of a flight where multiple critical tasks need to be performed quickly and the time simply doesn't exist to laboriously go through a checklist for the moment.  For instance, an high performance airplane making its takeoff roll on an instrument departure and climbout on a published departure will make use of workflows to set the plane for climbout and and handle all high workload tasks e.g. trimming, power settings, radio frequencies and communications with departure control, monitoring aircraft systems and engines in congested airspace, etc.  Checklists will then be utilized by the crew as time and workload permit doing so.  This was confirmed by a friend of mine who flies Dash 8s for American Eagle.
Workflows are useful in emergency situation, particularly those at low altitude, on takeoff and climbout, etc, where the time may not permit carefully running through a checklist to handle critical items, though emergency checklists will be use, again, if time and workload permit.
A checklist is just that - a list of items which the manufacturer recommends be checked and set a certain way during each aspect of flight.  But the pilot's first responsibility is to fly the airplane and not get caught up reading a list at a critical time.  Flows serve as a stopgap measure to set critical systems until a checklist can be reviewed properly.

Flows are not a "shortcut" to avoid checklists.  They are a natural progression of important items to check, that allow you to think of the whole system represented by each item on the list.  See http://studentpilotnews.com/2013/11/27/one-checklist-works-every-airplane/ and http://www.flyaoamedia.com/aoa/the-mystery-of-flows-vs-checklists/ to see how to use both together.

please add here the relevant content of your links, other sites may disappear, making your answer less useful.

Flows are basically ways to avoid doing checklists. If you use a checklist you do not need a "flow" because the checklist determines the order of items to be checked so a "flow" is completely superfluous. The "flow" is just a way of checking things ad hoc without using an actual list to save time.
The reason why commercial pilots use "flows" is because if they used a checklist for a lot of activites (which they should do) it would take too much time. Seriously, do you want 300 people waiting at the gate and leaving 20 minutes late because the pilot is still working through checklist number 7 and making sure the backup oxygen tank is pressurized or whatever? Using "flows" becomes a matter of practicality.
Where flows become really dangerous is on those private jets where some arrogant CEO is demanding they take off "right now" and the crew starts doing "flows" and skipping checklists. A perfect example is the Gulfstream IV crash last year that killed Lewis Katz, some media mogul, and six other people. The pilot failed to disengage the elevator gust lock. That's the kind of thing that happens when you start doing "flows".
-------------------- concerning flight crews not using checklists
One of my commenters seems to have the idea that "professional" flight crews always do complete checklists. This is just completely untrue. I gave examples in my response comment. Also, I will add another example here: Once I was a passenger in an AA 737 and there had been severe winter storm and the plane was badly iced. So, we spent at least an hour sitting there waiting for the de-icing to be completed. It's done and the flight crew just taxi-ed out and departed without checking anything. I almost interrupted the departure to talk to the captain and ask him, "Are you jerkoffs going to inspect the wings and empennage or should I?" For them to just depart with no inspection with such bad icing conditions was just incredibly stupid. (See here for typical crew procedures after icing: https://www.boeing.com/commercial/aeromagazine/articles/2010_q4/2/)

Uhhh... actually... yes.  I want the pilot to do every item on his/her checklist and definitely that backup oxygen tank should be pressurized if that's what someone has determined should happen, and it was important enough to include on a checklist.  Some things aren't on the checklist, some things are.  The things that are, are important enough to be.  So yes, I don't want anything skipped.  If this was standard operating procedure, we wouldn't wait an extra 20 minutes at the gate: the pilots would arrive 20 minutes earlier.

This is just not true. Professional pilots use checklists. A professional pilot that does not use a checklist when one is specified, will quickly become an ex professional pilot. The time used to run through checklists is accounted for in operations. It has to be.

@Jpe61 That is simply not true. I already cited the Gulfstream accidents as a typical example of professional pilots not using checklists at all. Also, I have many times seen commercial ACPs show up at a gate get in the cockpit without doing a walkaround and then departing faster than a checklist would allow for. Also, I have many times been in a cabin when a replacement flight crew arrived, entered the cockpit and then NEVER entered the cabin. To do certain items on the checklist for virtually all planes, including 737s requires entering the cabin.

@TylerDurden This answer is just plainly wrong! Professional pilots use flows followed by checklists. Of course there are examples where professional pilots took shortcuts (a famous example is HCY522, where the crew skipped an important checklist item and paid with their lives), but in general both flows and checklists are rigorously followed. As Jpe61 said, crews violating these principle will be quickly fired.


text:
Is there a European equivalent of VFR Flight Following?
In the US, Flight Following is a radar service provided to VFR aircraft on a best-effort basis. Controllers provide traffic advisories but they don't issue clearances or instructions and the pilot is responsible for maintaining separation from other aircraft, observing altitude, airspace and other flight rules etc. Flight following is only provided when the controllers' workload permits and it may be terminated at any time.
Is there an equivalent service in Europe? I've heard of something in the UK called "basic service" but I don't know if it's the same thing and if it's UK only or a Europe-wide service.

In Australia, it's called Flight Following http://www.airservicesaustralia.com/flight-briefing/pilot-and-airside-safety/working-with-atc/

In France, there is the SIV https://www.sia.aviation-civile.gouv.fr/dossier%5Caicfrancea%5CAIC_A_2011_01_FR.pdf

Yes, it is called Flight Information Service (FIS). FIS is defined by ICAO, and the term is used in most of the world. "Flight following" is a local term used only in certain countries.

A flight information service (FIS) is a form of air traffic service which is available to any aircraft within a flight information region (FIR), as agreed internationally by ICAO.
It is defined as information pertinent to the safe and efficient conduct of flight, and includes information on other potentially conflicting traffic, possibly derived from radar, but stopping short of providing positive separation from that traffic.
Flight Information also includes:

Meteorological information
Information on aerodromes
Information on possible hazards to flight

FIS shall be provided to all aircraft which are provided with any air traffic controller (ATC) service or are otherwise known to air traffic service units. All air traffic service units will provide an FIS to any aircraft, in addition to their other tasks.

And, in Europe, you will be charged for that service.

There is no charge for using Flight Information Service.


text:
What does LNAV engagement exactly mean?
I notice the term LNAV engagement being frequently mentioned in aviation related discussions or in several FAA's relevant material. Take, for example, this quote from Order 8260.58A (PBN Instrument Procedure Design) which states:

Order 8260.58A [5-1]: The ICA must be long enough to allow LNAV engagement (500 feet above airport elevation).

I am aware that LNAV means "Lateral NAVigation" but I have some trouble understanding what does "engagement" exactly mean and why an aircraft have to climb at 500 feet above airport's elevation before the initial turn for this engagement to happen. Could someone point me in the right direction?

In that context, "engagement" refers to transfer of control of the airplane to the autopilot.  Transport aircraft will generally have a limitation that forbids autopilot engagement on departure below, say, 500 or 600 ft.  Once it's engaged in NAV mode, the A/P needs a bit of time to sort itself out and start turning to follow the LNAV guidance.
So the design guidance there says that the lateral space allotted for the initial climb area for obstacle clearance has to take into account the behaviour of the aircraft when A/P is engaged at the minimum altitude allowable, in terms of the potential lateral real estate consumed to get on the proper departure track.

Some old aircraft (737 Classic comes to mind) don't allow arming LNAV/NAV AFDS mode on the ground, as you normally have to be at least 400ft above ground (ICAO PANS OPS says 396ft) before making turns more than 15 degrees, at which point you would engage LNAV. I guess the regulation takes old aircraft into account.
On the newer aircraft, you can arm LNAV/NAV mode on the ground already and it normally becomes active at 50ft.


text:
Why runway 13L/31R of JFK Airport does not mention any Threshold Crossing Glide Path Height for its reciprocal end?
I am studying FAA's airports legacy file and its corresponding layout data. I noticed that runway 13L/31R of JFK Airport lacks a Threshold Crossing Glide Path Height, as one can also confirm from this site. Is there any "standard" value that one can apply here? Neither the official aforementioned legacy file nor any relevant website mention a Visual Glide Path Angle either.
In comparison, runway's base end mentions both a Threshold Crossing Glide Path Height (74' AGL) and a Visual Glide Path Angle (3.00 degrees).
I would be grateful if someone could point me in the right direction.

Do you have information on the TDZ (touchdown zone) for the runway and glide path angle? You should be able to calculate the threshold crossing height with those two data points.

It provides the Elevation at Touchdown Zone, but no Visual Glide Path or any other relevant values.

I’m curious as to what you’re calling the “base end”

According to the layout of the airports' legacy file, the base end is the "13L" point of the runway, in other words the first point of the runway's segment when it is set to "13L" configuration.
From legacy file:
"BASE END IDENTIFIER: THE RUNWAY END DESCRIBED BY THE FOLLOWING INFORMATION. RELATES TO THE FIRST PART OF THE RUNWAY IDENTIFICATION (EX. FOR RUNWAY 18/36 THE BASE END IS 18)".

@RonBeyer could you help me understand how to calculate the threshold crossing height from elevation at touchdown zone and glide path angle?

@VectorZita You can't calculate it with those two points, you need the TDZ (how many feet from the threshold) and the glide path angle. Using some simple trig, you can then calculate the height above the threshold where the glide path crosses. You can't do it with the "TDZ height" because that is the elevation of the TDZ, it has no relation to the distance from the threshold.

@RonBeyer thanks for your answer, unfortunately I can not find any information regarding TDZ, either on an iap's plate or in faa's legacy files. They only mention threshold crossing height, glide path angle and elevation at touchdown zone.

That information is shown on the approach plates

It appears that 31R is not equipped with a VGSI. At least not that I can find. That would be why the data is missing.

On 13L the GS and VGSI are both 3°, but since the VGSI is located about 300ft further down the runway than the GS antenna the TCH is higher.

The better question here is why doesn’t 31R have a VGSI.


text:
Why is there a need for a Top Altitude in FAA's SIDs?
I am examining some of the FAA's SID charts and, as far as I can deduce, each SID provides information concerning the altitude when it is necessary and, if not changed by the controller, each transition/route description will end with something such as "Maintain X altitude etc." which seems that it is the same as the Top Altitude.
Since this information is written in SID's textual description as "Maintain X altitude", why is there a need to exist also separately as Top Altitude?

I'm not sure what you're asking? The description page is just clarifying and reiterating the info on the graphic depiction. Are you just asking why they put it on there twice?

Yes, but I guess what you said ("The description page is just clarifying and reiterating the info on the graphic depiction") answers that. So both the Top Altitude and the "Maintain X attitude" textual description refer to the same thing?

That's what I believe.

@TomMcW thank you for your clarification, please feel free to post your comments as an answer, so I can mark it as the accepted one.


text:
Is there a database from which I can retrieve the Expected Crossing Altitudes of a Departure or Arrival Procedure?
I am stuyding FAA's Coded Instrument Flight Procedures (CIFP) file which uses ARINC 424 digital format to code its data. I noticed that only mandatory crossing altitudes and speeds are included in the coding of the Arrival procedures (STARs), whereas expected crossing altitudes and expected speeds are omitted.
Take for example JFK's CAMRN arrival procedure. There are two assigned expected altitudes and one expected speed: at HOGGS (FL180) and at CAMRN (11000, 250K). The corresponding coded procedure in the CIFP file is:

Is there any reason that these values are omitted? Is there any other source where I can find these missing values? One would think that the expected crossing altitudes and speed are an important part of a procedure and thus I find it difficult to understand why they are not included in the CIFP file.
If I would like to study an arrival procedure's vertical profile but there aren't any assigned crossing altitudes, what is the most appropriate way for estimating actual, or, at least, realistic crossing altitudes (e.g. for design purposes)?

In STAR procedures, the crossing altitude and speeds are only specified when necessary for obstacle clearance and airspace purposes. It's up to the pilot to choose and calculate the optimal descent and speed for the approach as long as the minimum altitudes and maximum speeds are adhered to.


text:
How are runways numbered?
I'm not a professional pilot, just an enthusiast, so this might seem obvious to others; but I noticed that airports don't use sequential numbering for runways, starting from 1.
Liverpool (for example) has runway 9/27; so how are these numbers assigned? Also, what do Left and Right signify?

See also: https://en.wikipedia.org/wiki/Runway

@abelenky I guess it's just one things I've never looked up before now! It's planes that interest me, not airports.

Someone needs to send this to Hollywood so they can stop talking about "Runway 47" or other such garbage occasionally

@SSumner well if you add another runway after having 63 parallel runways all going north, 47 is next in the bag...

An extremely informative video on the topic : https://www.youtube.com/watch?v=H701DOaQvDM

I thought questions that lacked basic research were banned?

@jwzumwalt This was one of the very first questions asked on the site (the 65th). The idea behind posting it was to initially fill our 'knowledgebase', so to speak. Also it has had a very high number of pageviews, suggesting that it is high on the Google ranking for these keywords. I've just requested it to changed to a Community Wiki, however :)

Well, it has me confused... but OK. I had the question "Who installed the first ejection seat" banned; I would have thought that had general appeal too. It seems to me someone with 9500 points is more than a naive "enthusiast".

@jwzumwalt there was a debate around that question, yes, but I agree with you that it should have stayed, exactly like this one. unfortunately you decided to delete the question and not bring the discussion to meta. also, please do not look at the fake internet points when deciding if one is an enthisiast or not.

How does such a rude comment by @abelenky stick around for 7 years? It's just plain gate-keeping.

Runways are usually numbered according to their direction, more precisely called runway magnetic bearing or QFU (see Q codes).
Consider a plane flying toward the runway on final approach in a day without any wind. Divide its magnetic heading by 10, round it to the nearest whole number and you'll usually get the runway number. For example, if the magnetic heading is 345° then 345/10=34,5, so the runway number will be 35 which will be a runway used for landings (and takeoffs) to the north.
Opposite ends of the same runway have different numbers, 18 (which represents 180 degrees) apart. A runway with 35  for landings to the north will have runway 17 for landings to the south. Even though these are the same strip of concrete, they are treated as separate runways by pilots and controllers.
If there are two airports near one another with runways at the same angle, sometimes one of the airports will add or subtract one from the runway number to help planes differentiate between the airports.
Occasionally a runway number will change when the magnetic declination angle changes in such amount, making the runway magnetic bearing divided by 10 and rounded to the nearest whole number increase or decrease.
Some runways in areas of large magnetic declination use true instead of magnetic headings for the runway numbers. This is not unusual in northern Canada and Greenland.
When there is more than one parallel runway at an airport, L, R, or C may be appended to the runway number for Left, Right, or Center. These are based on the approach direction, so, for example, the runway 35L would be called 17R from the opposite direction.

Yes, the Runway numbers at PAO changed from 12/30 to 13/31 around ten years ago or so.

Just a remark, I believe that the 4 runways of CDG are all parallel, just numbered one-off. So your 3rd paragraph can apply to a singe airport, too.

@tohecz Not quite: they appear to be parallel but, according to Wikipedia, they're numbered 08L/26R, 08R/26L, 09L/27R and 09R/27L. The six runways at Denver International are 16L/34R, 16R/34L, 17L/35R, 17R/35L (all parallel) and 7/25 and 8/26 (parallel to each other, at right-angles to the other four but presumably not labeled as an L/R pair because they're at opposite sides of the airport). Meanwhile Chicago O'Hare's runways include the parallel 9L/28R, 9R/27L, 10L/28R and 10C/28C but no 10R/28L -- I guess it used to exist but was closed?

I would add that some airports far north have runway with suffix T (e.g. 17T/35T in Resolute Bay) meaning the number is derived from true heading rather than the usual magnetic heading.

KATL has 9R/9L and 10R/10L, which are all parallel. Presumably after 3 parallel runways they drop the "Center" designator?

L/C/R tends to be used when the runways are close enough that a pilot needs to know that when he breaks out of the clouds there will be multiple runways in front of him and he has seconds to figure out which he’s supposed to land on. Add/subtract one is used when they are far enough apart that confusing them is unlikely—or when there are more than three parallels (very rare).

Runway numbers are determined by their heading, e.g. for Liverpool, runway 9/27 is facing approx. magnetic heading 90° in one direction, and 270° in the opposite direction.
If an airport has parallel runways, these would then be marked Left, Center and Right, e.g. 9L/9C/9R.
Heathrow has two parallel runways, the 'right' runway has 09 R on the east and 27 L on the west end (and the other is 09L/27R).

An interesting follow-up to this is that sometimes runway numbers change! The surface of the earth is not stationary, it moves small amounts over time and over larger periods of time, it can move enough that a runway's direction can shift to where an increase or decrease in its number is warranted.

A minor point, but I think the headings are magnetic rather than true.

@mah The reason for changing designations is more or less all about magnetic pole movement rather than continental drift.

It's not "more or less", it's a fact. Runway numbers can be changed if the magnetic variation changes (so if the location of the magnetic poles change position). So if runway 26/8 has a magnetic heading of 264.9˚/84.9˚ and it changes to 265.2˚/85.2˚, it will probably be renamed to 27/9

@PhilippeLeybaert Ah, that cleared a confusion I had. Since the magnetic poles can change, I always thought what happens when they change significantly.

BTW, what would happen when the magnetic poles will shift in future, i.e. Pole reversal

@user1994911 Thanks for the info on magnetic vs true, I've added it to the answer!

@Farhan: From the article you cited: "Most reversals are estimated to take between 1,000 and 10,000 years.".  At best, a runway's heading could flip 180 degrees over 1,000 years(0.18 degrees/yr) which is changing the runway number every 55 years.

@PhilippeLeybaert well, continental drift might be a factor every few million years :D

@Farhan That's quite a theory. I would bet with you that humankind won't see it hapenning :) OTOH, it's not really the pole that is significant, the magnetic field is not really like from one big magnet, more like from a large bunch of small magnets, so the local variations can be quite big and irrelevant of what the pole is doing.

@abelenky: But what is the intermediate state during the reversal? The field could slowly rotate, but I would expect more that it would weaken, disappear altogether for short while and reappear with opposite polarity. In which case the numbers wouldn't change gradually. Instead for some time magnetic compass would become useless for navigation and other reference would be devised.

@Jan Hudec:  The last time a pole reversal happened was approximately 750,000 years ago (well outside human history).  I do not think the FAA has, nor needs, a plan for a numbering scheme during a reversal.

The information from the US AIM may be useful here:

b. Runway Designators. Runway numbers and letters are determined from
  the approach direction. The runway number is the whole number nearest
  one‐tenth the magnetic azimuth of the centerline of the runway,
  measured clockwise from the magnetic north. The letters, differentiate
  between left (L), right (R), or center (C), parallel runways, as
  applicable:
1. For two parallel runways “L” “R.”
2. For three parallel runways “L” “C” “R.”

As to why the runway is actually constructed on heading 1, 9 or something else, that is determined by the local prevailing wind conditions among other considerations (terrain etc.). Aircraft always take off or land into the wind (as far as possible), so that is a key factor in how runways are positioned. NASA has a very good article on airport layouts that goes into more detail.

Some times, like KMIA, you face 3 parallel runways, but these are designated as 08R, 08L, and 09. Just because the runways 08R and 08L are 'grouped'.

@YvesKlett Indeed, the ILS/LOC approaches for 8L, 8R and 9 at KMIA all show 092 as the final approach course. I have no real idea why, but my guess would be that since there is a large distance between 9 and 8L/8R, using the same number for them all would be confusing, especially in limited visibility. There are also procedural differences based on the distance between parallel runways; perhaps the numbering helps to manage/implement that too.

Runways are numbered based on compass heading.
(Note that within the US, we use MAGNETIC heading; this is not necessarily the case in other countries! (e.g: Canada, which is closer to the north pole, where they use true north to compensate for compass north being off)
(Meaning each physical runway is two numbers!)
The heading of the runway is rounded and truncated to the first two digits; For example, a runway with a heading of 093 degrees becomes runway 9. (Runway 27 from the opposite end).
Now you may ask, what if there are 2 parallel runways?
One becomes runway 9L (left) and the other becomes runway 9R. A third runway would cause one to become 9C (center).
But what if there are MORE runways on the same heading? (Such as the 4 at Harstfield-Jackson International Airport in Atlanta?)
In this case, the airports will typically change the number of the runways by one, even though the actual heading of the runway may be no different! (For example, you would now have runways 8L, 8R, 9L, and 9R that are all parallel.
Wouldn't this cause problems with pilots not knowing the actual heading of the runway though?
(Remember that the headings are rounded, and based on magnetic (less accurate) headings!)
One of the pieces of information about airports that is published on charts and such is the actual heading of the runway.
Grass runways are suffixed with a G (E.g. 12G), although since a pilot usually isn't going to have any trouble identifying a grass runway the G is not usually marked. I can't speak to the numbering of water runways; I have limited experience with amphibious aircraft, and I find it highly implausible that they paint the runway numbers! ;)

I wasn't sure whether or not "water runways" was a joke, so I looked up whether or not there really is such a thing. Turns out there is; the David Wayne Hooks Memorial Airport (KDWH) in Spring, Texas has one.

@TannerSwett Water runways used to be much more common, when international travel was typically by flying-boat rather than a heavy airliner (for which suitable runways were rare).  They can be found on historical coastal charts.

The suffix indicates type of runway not surface type. S = STOL runway, G = glider runway, W = water sealane or waterway, and U = ultralight runway.

@TannerSwett Notably, KDWH has 17R/35L, 17L/35R, and 17W/35W, with the latter not being parallel to the former two despite the numbering.

Runway designations are defined by ICAO Annex 14. More than 3 parallel runways on the same bearing would have the runway identifier adjusted up or down for the ones in excess of 3, to ensure uniqueness. In other words, if there were 9 parallel runways all true north, they would be designated 35L, 35C, 35R, 36L, 36C, 36R, 01L, 01C, and 01R. The runway number is always two digits. The runway designator is always unique at a given airport. The use of the 'T' runway suffix to designate true, while possibly still existent on the physical marking of the runway, is no longer used in the industry. These rules limit the number of runways at a given airport to 108.

I would be most interested to see an airport where the maximum number of runways numberable was becoming a factor!

A can think of a few dry lakes...

"These rules limit the number of runways at a given airport to 108." Only if you count the reciprocal as its own runway. If instead you count slabs of ground, which makes more sense for figuring out aircraft movements (hello Tenerife), then the maximum number is 54, because you can have 18 (for example 01 through 18 inclusive, with the reciprocal being 19 through 36 inclusive) sets of L/C/R, for 18x3 = 54.

Runway numbers are given as per their direction on compass. Only difference in compass reading and airport runway numbers is that compass reading may be in 3 figures like 120 or 230 etc, but runway numbers are in 2 digits for universal understanding and ease in understanding without confusion.
It is simple: when an aircraft is taking off or landing on a runway that has been assigned, say 09; it will mean that when the aircraft would be ready for take off or coming in for landing, its compass reading should indicate 090 (Last digit is not advised as it is understood as zero)
Similarly if an aircraft coming in to land on, say, runway 25, on lining up with the runway while in the air, the aircraft compass should read 250 degrees. Some airports show single digit as runway number, (like 3 or 7). In such cases a zero is to be added before and after the number. Hence 3 will mean 030 and 7 would mean 070.

Nice first answer - one thing worth noting is that the compass reading might be off by a few degrees, i.e. indicate a heading of 092 for runway 9.

This is incorrect. The last digit of the aircraft's heading is not assumed to be zero: the heading of an aircraft taking off from runway 09 could be anything between 085 and 095. In fact, it could be even farther from that because airports quite often have a runway that, for example, "should" be labelled 08/26 but is labelled 09/27 to avoid confusion with some other runway 08/26.  (E.g., at Denver, runways 07/25 and 08/26 are actually parallel.)


text:
What are the Single European Sky (SES) and Functional Airspace Blocks (FABs)?
Air Transport World is reporting that the European Commission has initiated legal proceedings against Germany, Belgium, France, the Netherlands and Luxembourg; for not implementing FABs by the deadline. A quote says:

FABs are a cornerstone of the SES initiative and are intended to reduce the capacity, cost and environmental constraints that continue to dog Europe's fragmented air traffic management (ATM) system by establishing common airspace blocks arranged around traffic flows rather than state boundaries.

What exactly are SES and FABs, in laymans terms?

SES = Single European Sky Legal Framework. It started in 2004 when the EU Parliament and Council adopted Reg 549/2004 (framework regulation), 550/2004 , 551/2004 and 552/2004 (interoperability regulation). Also, a very important regulation was 219 which established EASA! (All these legislation is called SES I... amendments later came in place along a myriad of Implementing Regulations) which dealt mainly with What and How the Air Navigation Providers (ANSPs) must provide ANS services. This legislation aims at Uniting the National FIRs (Flight Information Regions) into BIGGER FIRs (Called FABs - Functional Airspace Blocks). Most of the operational advantages of FABs: Direct Routes, lower CO2 emissions and lower fuel burns for air companies are True and EU citizens will gain overall.
Since FABs will include the airspace of more sovereign nations, from a legal point of view, FABs need to be created with a Multilateral Agreement in the adjacent States.

To me this reads a lot more like a rant about SES and EU politics than an answer to the question. Perhaps you can edit down to simple factual statements answering the key questions ("What is SES? What are FABs? How are the two related?")

voretaq7 ...specially for you: SES is a part of EU legislation, FAB is a concept comprising multiple FIRs. According to SESI, States in the EU are required to create FABs. I think this is all you need to know if you're not a EU citizen.

the point of my comment was that you should edit your answer to provide that information (and de-rantify it).

Agreeing with @voretaq7, this is a rant, not an answer to the question which was "What exactly are SES and FABs, in laymans terms?"

@voretaq7: The information in the rant is still relevant as answer as it explains the reason for the report quoted in the question. It should be worded neutrally, but I think it should be here.

@JanHudec It's the tone that I have a problem with: We're an aviation site, not a politics site, and if we start getting "ranty" it can turn off a lot of potential users. (It also seems like an incomplete answer - it explains nothing to me, the non-EU pilot, about what these things mean if I decide to go fly in Europe - but that could be because the rant is obscuring the info.)

@voretaq7 how the FABs and SES regulations will affect non-eu pilots is a completely different quesiton. and I'm sorry to to hear from pilots that my  answer is a rant about politics, but it's TRUE, SES and FABs are political things to start with, they are about regulations. ICAO is also about regulatioins. and I know from my experience that pilots don't like regulations, but it's not my fault :)


text:
Are aircraft sounds publicly available in a repository?
Referring to the automated callouts and sounds made by the fwc, tcas, gpws, pws, etc. — are these available to download in one repository at all? For any aircraft, Airbus or Boeing.
Understandably, these may not be freely available, but I'm curious otherwise too (e.g. the likes of Air Crash Investigation must do this).

This is really more of an Audio/Video question.  Yes the sounds are of airplanes, but the main gist of the question is sound as it relates to audio recordings...

See also: Should we allow questions asking for resources?

Right, but you aren't asking for an aviation resource here you're asking for an audio resource (at least that's my opinion).  Understand, my purpose in pointing this out is to try and get this question to a group that can be more helpful, like a forum or stack that deals with recorded audio.

One place to look is models of the planes for flight simulators. There is generally a "sounds" folder of some sort inside the airplane folder that includes some cockpit sounds.
I'm guessing the original files are proprietary and there is really no reason for the companies to freely share them. Shows like Air Crash Investigation might get access to a simulator that can make all the real sounds.

I did a quick google search and this was a link that I found.  Although, the quality of these samples leaves a lot to be desired.


text:
Do aircraft carriers always face into the wind?
When landing at a normal ground airport, the runway facing the compass point nearest to the heading of the wind is always operated, so that aircraft landing and taking off alway have to use the least distance of runway as necessary.
On an aircraft carrier the whole ship can rotate; so do they typically always face into the wind? How often do they rotate the ship if this is the case?

During flight operations, the aircraft carrier strives to maintain 30 knots of wind down the angle of the flight deck.  Generally speaking, the carrier will adjust its speed and course through the ocean to maintain the desired winds.  However, shifting winds and the sheer magnitude of the carrier may mean that the winds are generally down the angle, but may involve a crosswind component.  Also, the structure of the carrier, because of its enormous size, actually influences the flow of the wind, and can create pockets of low pressure in the approach where high sink rates can develop.

Note as well that most if not all modern carriers are capable of making 30 knots or better through the water, which is where your baseline figure comes from.

@NathanTuggy 30kts isn't a baseline number, its the only number, and it's been this way for decades.  Its irrespective of the carrier's max speed.  Of interesting note, I believe there were WWII carriers capable of traveling 30kts.

Sure. Maybe I should have left out "modern", but most of what I know is USN-specific. (The first nuclear carrier in the early 50s could do well over 40 knots, and was limited more by escort speed and hull strength [!]) than by power.)

As I know minimum is 26kt, not30

Moreover many carrier has speed lower than it,from USA first carrier Langley to the latest assult ship America

@NathanTuggy - that 40-knot carrier is a myth. Enterprise could do maybe 34. Her propulsion was the same as older 33-knot steam carriers and could never, with no amount of power, do much over 34. The difference was that she could do 30 all day long.  An article: http://navweaps.com/index_tech/tech-028.php

@Therac: Perhaps I will need to give Tom Clancy's Carrier a bit of side-eye, then, as I believe I got this figure from that book, although it's admittedly been a long time since I read it. (It is not fiction, or at least is not intended to be.)

Not answered yet is this part of the question:

How often do they rotate the ship if this is the case?

First, just a nomenclature alert: ships don't rotate, they maneuver, steer, or change course.  And the answer to your question is: whenever necessary.  It is a big ocean and unless there is an island or something nearby, they always face the wind for air ops.  Note that with the angle decks, they want the wind coming directly down the angled deck so the ship is actually heading a little off to the right of the wind to accomplish this.


text:
Do helicopters fly the same instrument approaches as fixed-wing aircraft?
Do helicopters fly the same instrument approaches as fixed-wing aircraft? If so, which approach category and minimums do they use?

Helicopters can fly the same standard IAPS.  The visibility minimum is the greater of
a) one half the Category A visibility minima,

b) 1/4 statute mile visibility, or

c) 1200 RVR

We use Category A's MDA/DH. See the AIM 10-1-2 for more information.
Also there are Copter IAPs (example here), and the viz/altitude minimums are stated on those plates.

Thanks, do you have a source for the minimums that you quoted? And is that the FAA regulation or another one? I'm not doubting your answer, I just haven't noticed many helicopter-specific procedures in the 'obvious' places, although admittedly I haven't searched systematically.

It's on FAR AIM 10-1-2.. Here's an example for a copter approach:
http://155.178.201.160/d-tpp/1411/00610COPTERR028.PDF


text:
Why should some piston engines not be run lean of peak?
Leaving aside the claimed pros and cons of lean-of-peak (LOP) vs. rich-of-peak (ROP), the C172S Lycoming IO-360-L2A handbook I have says "Continuous operation at mixture settings lean of peak EGT is prohibited", and indeed I was always taught to run the engine ROP.
Obviously you should always follow the POH for your aircraft, but considering piston engines in general, why would running LOP be prohibited?

Considering piston engines in general there's a few reasons not to run "lean of peak", but the arguments I'm aware of all fall into three broad categories:

Poor Instrumentation
Most folks advocating Lean-of-Peak engine operation will also tell you that you need a good engine monitor (with Exhaust Gas Temperature (EGT) and Cylinder Head Temperature (CHT) probes for each cylinder) so you can ensure that all your cylinders are operating within safe temperature limits.
Manufacturer CHT/EGT systems are often "single-probe". On the IO-360 in your Cessna example that leaves you with a 3 cylinder blind spot in your monitoring, and the potential risk of damaging your engine based on the incomplete information you have.
Uneven mixture distribution
Some engines simply can't run lean of peak because of uneven mixture distribution: Either the engine will get rough as some cylinders "miss", or you'll have some cylinders lean of peak EGT and at a safe cylinder head temperature while others are redlining their CHT and potentially causing damage to your engine.
This sort of uneven mixture distribution happens frequently in carbureted engines, but there are many injected engines which also have poor fuel distribution & significant variation in mixture between cylinders (This is where GAMIJectors makes their money - by providing balanced injectors to even out fuel distribution).
"In Case Something Breaks"
Hypothetical scenario: you are cruising at 8000 feet, you've leaned for cruise, and your mixture control suddenly fails in such a way that your engine is stuck at the current mixture setting.  All the airports within your endurance range are roughly at sea level.
An engine running lean of peak may begin to run rough as you descend for landing (the mixture becomes too lean to support combustion).  An engine running rich of peak may continue to run acceptably through the descent. (The mixture may transition into "the red box zone" where operation at high power settings are dangerous, but you'll theoretically be reducing power for your descent, so the chance of doing damage to your engine isn't that high unless you have to perform a go-around or other high-power maneuver.

A prohibition on Lean-of-Peak operation in your POH is probably historically based on #1 or #2 above -- the manufacturer doesn't want to advise you to do something that might damage your engine.  Running Rich-of-Peak is conservative operating guidance, where the downside is slightly increased fuel consumption and the possibility of fouling a spark plug (which is not likely at normal operating power settings) versus the downside of potential engine damage from improper Lean-of-Peak operation.

The most direct answer to your question has little to do with physics and a lot to do with a typical pilot's understanding of how a piston engine works.  The manufacturers specify ROP because it's "easy."  Most pilots (myself included, over the course of 2900 hrs of flying) were not exposed to the whys of proper engine operation during training.  We were all taught the "LOP = burned valves" which simply isn't true.  The manufacturers compensate for this lack of understanding by oversimplifying engine operation directions to keep us safe from ourselves.
Contrary to popular belief, LOP is not bad for piston engines.  What is bad is mixture setting within what is commonly referred to as the "red box."  Running LOP safely requires you to lean further than what most standard fuel injectors can support.  Leaning with unbalanced ("standard") injectors will eventually lead to a rough running engine that would otherwise run just fine ROP.  This is where Gami or Continental balanced injectors become necessary.  They are precision injectors that allow you to lean far enough LOP while still delivering even amounts of fuel to each cylinder to keep the engine running smoothly (oversimplified).  Google "mixture setting redbox" to get started.  Note that you can be ROP and still inside the red box.  ROP alone is no guarantee that you're running the engine properly.
There is a TON of research out there that will lead you to the conclusion that LOP is not bad when set properly (just as ROP is fine when set properly).  In fact, in most cases the engine will run cooler and cleaner LOP than an identical engine run ROP.  Mine does.
I strongly recommend that you read the following several times:
Pelican’s Perch #63: Where Should I Run My Engine? (Part 1)
Pelican’s Perch #64: Where Should I Run My Engine? (Part 2 – The Climb)
There is a third article in the series but the site won't let me post it...need more reputation!
(edit: Pelican’s Perch #65: Where Should I Run My Engine? (Part 3 – Cruise)) +
(edit: Pelican’s Perch #66: Where Should I Run My Engine? (Part 4 – Descent))
I fly my IO-520 LOP in cruise (waaaay ROP in the climb) and see about 1.5gph savings compared to my POH fuel burn.  It costs three or four knots but that's a fair trade!  My 1470 hour Continental clyinders hold great compression and I burn very little oil.  I use an EDM700 engine monitor and Gamis.  Do not be afraid of LOP, just learn how to do it correctly!
Happy flying!

Another poster already linked to 2 articles from the "Pelican's Perch" series.
Although this discussion is 4 years old, I'd like to add the 3rd link that acpilot probably wanted to post:
"Mixture Magic"
https://www.avweb.com/features_old/pelicans-perch-18mixture-magic/
This article can be seen as a prequel to the other two, starting with the basics and later making the points for running LOP:

Why leaning is important (safer engine operations, less fuel consumption)
Basics of combustion and mixture
Uneven mixture distribution is

the cause of the "shaky engine" when you lean too much
reducible only with fuel injection
why you need an EGT/CHT monitor on all cylinders (see other answers here).

The relation of power, fuel flow, EGT and CHT and how to interpret plots of those variables; this is where Deakin gets to the point that

there are points of similar power but with less fuel consumption and cooler temperatures on the lean side of the EGT curve.
the idea of "taking the throttle back a bit" right after takeoff on normally aspirated engines is a bad idea (CGT gets higher instead of lower)
using an engine monitor, go LOP using the hottest cylinder as your reference.

Money Quote:

For high power, maximum-performance operation, you should run richer
  mixtures and higher RPMs. For low power, maximum-efficiency operation,
  you should run leaner mixtures and lower RPMs.

Deakin answers OP's question implicitly in this article supposing engine manufacturers wanted to be on the safe side (emphasis by me):

It appears to me that running in accordance with the POH will provide
  good results in the worst possible cases, and TCM probably felt this
  was their best option.

This and the other two articles convinced me back in the day to fly LOP (on an IO 360 A1A, EDM 700 monitor, fuel flow meter). That gave me a smooth cruise with ~ 10% less fuel consumption.
FWIW, I read all of John Deakin's articles on AVweb and highly recommend them. They provide great insight from a aviation veteran - sometimes grudgy but mostly substantiated with sources as far back as the Wright Co.

It would be great if you could summarize the main points of the articles; we generally don't like link-only answers here because they can end up broken.

@Pondlife, I elaborated a bit on the contents of the article.
In case of broken links, I checked that the articles can be retrieved from the Internet Archive.

@Fly Guy...good stuff.

The lyc O-320 happens to be prone to exhaust valve guide wear. Heat accelerates wear. Running LOP generally causes the exhaust valve to run hotter than running ROP and wear out much faster.
In an ROP environment, the extra fuel that is not burnt lands on many of the top end components including the exhaust valve. As it evaporates off the surface or out of the fuel/air charge, it cools the component or charge slightly (kinda like water evaporating  off your skin cools it down).
May not sound like much, but it makes a big difference in the rate of wear of top end components.

Is that why automakers tended to run engines rich (late 60s, early 70s)? I think that the ultimate objective was to reduce NOx emissions by keeping temperatures down. However, that led to miserable fuel economy, which bit automakers (especially in the US) when the '73 Embargo hit.

The EGT at 50d ROP is exactly the same EGT @ 50 dF LOP. The same temperature. It is not cooler at LOP or warmer at ROP.
The CHT at EGT of 50d ROP is significantly higher than the CHT at EGT of 50 dF LOP.
No LOP operation can harm the cylinder being monitored,as the ICP and the CHT is always lower at any time during LOP operations.

Welcome to aviation.SE! Can you expand a bit on your answer? You say that LOP operations are never harmful, but then why does the manufacturer prohibit LOP operations in the case I mentioned?

Some real good / sound detail here.http://www.advancedpilot.com/articles.php?action=article&articleid=1838

APS is good but I don't see a reason to spend $1,000 to learn what has already been explained wwll online.  Deakin is the man!

Running too far lean of peak is bad for the engine. That's easy to do if the mixture isn't precise enough, or if you descend and forget to adjust the mixture. If there's not much leeway in a particular engine or if the engine is susceptible to damage from running a little too far lean of peak, the manufacturer will prohibit the practice.

How can running "too far" lean of peak be bad for an engine? The further LOP you go, the cooler the engine runs. Unless you mean that the engine will eventually shut down...

I have had a Bonanza A36 and a Piper Archer in which the POH said not to lean too far or you may damage the engine. I'm not sure about newer engines.

The IO-550-B (or IO-520-Bx) in Bonanzas and the IO-360 in Archers can be run LOP regarless of age.  Any piston engine is LOPable...physics does not distinguish between engine makes and models.  The idea that LOP is bad is absolute nonsense.

The manual did not say LOP is bad. It said too far LOP is bad. I don't know why.

Generally, slightly lop is bad (>65% power).  Further lop is ok unless the fuel distribution is such that the engine cannot run smoothly.  The red box depicts the "dangerous" areas.


text:
Are taxiways always one-way towards a specific, fixed direction?
I was studying the airport diagram of JFK and I began to wonder if aircrafts use taxiways as a one-way road. In case they do, is the direction of a taxiway fixed or does it change according to the daily needs of the airport?

At any given moment they are generally one direction as planes cant really turn around like cars but the taxi way its self can typically support traffic in either direction. Airports do have a "flow" to them but it depends on the runway they are using as well as the direction of departure of that runway. If the wind shifts and the approach is taken from the opposite direction the controllers will "turn the field around".
This time-lapse video shows the principal pretty well, the aircraft are pushed out onto the ramp form the jet bridge, nose towards the taxiways. They then head out to the departure end of the runway all following generally the same path. They queue up and depart when cleared. If the wind were to shift around they would do so from the other end of the runway which would reverse the flow (generally speaking) on the field.
You can find the FAA's advice on designing taxi ways here.
At uncontrolled airports the pilot can turn the field around.

At KBFI, (Boeing field) the taxiways are big enough for big planes like the 747.  But there are also flight schools at the field with Cessna 172s.   It is common to get instructions like, "N123 & N456: Both stay to the right side of the taxiway for opposite taxi-traffic; you'll pass each other near Alpha-8"


text:
Can some IAFs be skipped if more than one IAF exists?

Take, for example, this FAA official IAP plate (ILS RWY 13L CAT II JFK). Its Initial Segment consists of more than one Initial Approach Fix (IAF): COVIR, KMCHI, and BUZON. As far as I can interpret this, when an aircraft enters from the en route structure, it is obliged to follow the route COVIR → KMCHI → BUZON → TELEX etc.
My question is, is the aircraft supposed to follow this particular route or, depending from where it comes, it can "skip" e.g. the first Initial Approach Fix, and follow the route KMCHI → BUZON → TELEX (instead of COVIR → KMCHI → BUZON → TELEX)?
Also, if the answer is yes, does that mean that it can even ignore all the IAFs and enter Intermediate Segment directly, provided that this serves its purpose better?

Any initial approach fix (IAF) is a valid point at which an aircraft can start the procedure. Many procedures also have IAFs on multiple paths to choose from to get to the final approach. Standard Terminal Arrivals (STARs) sometimes include a certain IAF so that pilots can go straight from the arrival to the approach. Aircraft not on one of these STARs could use any other IAF.
Aircraft can also start even later in the procedure at an intermediate fix (IF), such as TELEX in the above example, provided it is coordinated with ATC and certain conditions are met.
After entering a procedure, aircraft are expected to fly the procedure as published. While it's not as common as with a SID or a STAR, ATC could certainly give an aircraft instructions for a shortcut on an approach, for traffic or other reasons. ATC would need to authorize this to ensure clearance from traffic and obstacles and compliance with restrictions such as noise abatement.

Thank you foot, just one more clarification: Apart from ATC vectoring orders, which can override the standard chart procedure, if a pilot is to choose the COVIR IAF, do the arrows imply that he "must" approach the intermediate segment by following the COVIR → KMCHI → BUZON → TELEX route? Or is there the possibility of "flying" from COVIR directly to the IF as desired?

@VectorZita At a big airport like JFK they will generally be on vectors by the time they reach the IAF. They are really just for NORDO situations. And ATC would expect you to follow each part of the procedure after the IAF. If you flew directly from COVIR to TELEX you would not be guaranteed obstacle clearance.

Clearance will be as directed by ATC at time of departure, or as modified by ATC while enroute.

Thank you CrossRoads for your input. Does this mean that ATC can request from the pilot to follow the route KMCHI → BUZON → TELEX, instead of the "normal" initial approach segment that is depicted on this particular IAP's plate (COVIR → KMCHI → BUZON → TELEX), or even ignore the whole initial segment and vector him directly to the intermediate segment?

Yes, your route will be directed by ATC to merge you in with other planes in the system.  ATC will often try to give you a more expeditious route if air traffic will permit it.  If you watch the traffic for JFK on Flight Tracker, you might be able to determine what routings are being used (might have to watch for a while) https://www.flightradar24.com/40.64,-73.73/12  or you might be able to determine from listening to a Live ATC website, try one: https://www.google.com/search?q=live%20atc%20jfk&cad=h

At the moment, planes from the south seem to flying northeast, past the airport, then turning left and landing to the southeast, which is not the approach you have shown above. Planes from the east are sort of following the southern shoreline then turning northeast to join the flow of planes from the south.

Click on a plane, commercial flights will show their take and destination and their flight path will be shown, and you can see other planes following the same flight path.